SLE is a systemic autoimmune disease characterized by profound B cell abnormalities and multiple autoantibody production. However, despite major advances in the field of human B cell biology, the precise antigenic and cellular mechanisms that underlie the activation, diversification and expansion of B cells in SLE remain poorly understood. Moreover, a precise understanding of the relative participation of different B cell subsets during acute disease exacerbations has been hampered by disease heterogeneity, imprecise B cell phenotyping and the lack of high-throughput technologies needed to define the antigenic forces driving the generation and selection of autoreactive B cells and serum autoantibodies. During the current ACE cycle we have established the tools required to address these questions including multi-dimensional flow cytometry; next generation sequencing (NGS); large scale single cell antibody generation; and bioinformatics platforms for the integrative analysis of high-density immunological, transcriptional and clinical data. Moreover, we have initiated collaborations with expert groups for the study of B cell and ASC epigenetics (Dr. Boss, Collaborative Agenda PI) and for the analysis of serum antibody proteomics (Dr. Cheung; CST). In this Principal Project of the Emory ACE U19, we proposed to build on these accomplishments to dissect the participation of B cell and ASC subsets through the following specific aims: Aim 1. Participation and antigenic selection of different B cell compartments in SLE flares using repertoire analysis by NGS and single cell antibody production; Aim 2. Relative contribution of short-lived and long-lived antibody secreting cells to the SLE serum autoantibody proteome; and Aim 3. Epigenetic and transcriptional control of SLE B cells in conjunction with the Collaborative Project. The work proposed is highly synergistic with the Collaborative Agenda and the Pilot Project and has a high degree of innovation in terms of the questions asked and the experimental approach. The expect results should be of far-reaching significance for our understanding of the pathogenic mechanisms acting upon B cells in human autoimmunity and for the rationale design of safer and more effective therapies.